Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage of the cells, through programming (which is sometimes referred to as writing) of charge storage structures (e.g., floating gates or charge traps) or other physical phenomena (e.g., phase change or polarization), determine the data value of each cell. Common uses for flash memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, cellular telephones, and removable memory modules.
Flash memory typically utilizes one of two basic architectures known as NOR Flash and NAND Flash. The designation is derived from the logic used to read the devices. Typically, an array of memory cells for NAND flash memory devices is arranged such that memory cells of a string are connected together in series, source to drain.
To meet demands for higher capacity memories, designers continue to strive for increasing memory density, i.e., the number of memory cells for a given area of an integrated circuit die. Typical flash memory devices utilize circuitry to sense the data state of memory cells. These sense circuits (e.g., sense amplifiers) typically include a reference current generator to provide a particular reference current in each of the sense amplifiers of the memory device. In order to provide a precise and low level reference current, what are often referred to as long body transistors, such as long body MOSFET transistors, are utilized in each of the reference current generators of each sense amplifier of the memory device. The number of sense amplifiers in a memory device is typically quite high. For example, a memory device might comprise 64,000 sense amplifiers configured to operate in parallel. Thus, a low level reference current is also desirable due to the parallel operation of the sense amplifiers in order to maintain a low overall current consumption of the sense amplifier circuitry. A large amount of area (e.g., real estate) of the memory device may also be consumed by the long body transistors used in each of the 64,000 sense amplifiers of the memory device. The long body transistors of the sense amplifiers might consume ⅓ of the total area of the sense amplifier circuitry of the memory device, for example.
For the reasons stated above, and for other reasons which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a reduction in the area occupied by support circuitry of memory devices, such as memory device sense amplifier circuitry.